Artificial intervertebral joint permitting translational and rotational motion

ABSTRACT

An intervertebral joint prosthesis having a ball component ( 22 ) for engagement with a first vertebra ( 26 ) and a trough component ( 24 ) for engagement with a second vertebra ( 27 ) adjacent to the first vertebra is disclosed. The trough component ( 24 ) includes a generally concave surface ( 50 ) having a substantially flat portion ( 52 ). When the ball component ( 22 ) and the trough component ( 24 ) are engaged to their respective vertebrae, the ball component ( 72 ) and the trough component ( 24 ) engage each other, permitting rotation and translation of the vertebrae with respect to each other. Both components include a flange ( 34,56 ) for engaging a vertebra. The invention also contemplates a method for and a tool for use in implanting a two-piece intervertebral joint prosthesis.

This application is a continuation of U.S. patent application Ser. No.09/534,767 entitled ARTIFICIAL INTERVERTEBRAL JOINT PERMITTINGTRANSLATIONAL AND ROTATIONAL MOTION, filed Mar. 24, 2000 by the sameinventors now U.S. Pat. No. 6,540,785, which is a division of U.S.patent application Ser. No. 09/177,317 having the same title, filed Oct.22, 1998 (now U.S. Pat. No. 6,113,637).

FIELD OF THE INVENTION

The present invention is directed to an intervertebral joint prosthesis.Specifically, the invention includes a device which is implanted inplace of degenerated or absent intervertebral disc tissue, and tools andmethods for implanting the same.

BACKGROUND OF THE INVENTION

In the treatment of diseases, injuries or malformations affecting spinalmotion segments (which include two adjacent vertebrae and the disctissue or disc space between them), and especially those affecting disctissue, it has long been known to remove some or all of a degenerated,ruptured or otherwise failing disc. In cases in which intervertebraldisc tissue is removed or is otherwise absent from a spinal motionsegment, corrective measures are indicated to insure the proper spacingof the vertebrae formerly separated by the removed disc tissue.Commonly, the two vertebrae are fused together using transplanted bonetissue, an artificial fusion element, or other compositions or devices.Fusion of adjacent vertebrae is a procedure that is performed many tensof thousands of times each year in the United States and Canada.

There is increased concern in the spinal medical community, however,that the biomechanical rigidity of the intervertebral fusion maypredispose neighboring spinal motion segments to rapid deterioration.See, e.g., B. H. Cummins, J. T. Robertson, and S. S. Gill, SurgicalExperience With An Implanted Artificial Cervical Joint, J. Neurosurg.88:943-948, 1998. For example, removal of the intervertebral disc andsubsequent fusion of the C3-C4 vertebrae may spur deterioration of theC2-C3 and C4-C5 segments. A spinal fusion prevents the fused vertebraefrom moving rotationally or translationally with respect to each other,as natural disc tissue permits. That lack of mobility may increase thestresses on adjacent spinal motion segments. Follow-up of patientsundergoing a successful fusion may reflect an incidence of neighboringsegmental disease as high as 20%, and indications are that 50% of fusionpatients will continue to have complaints of pain. Several conditionshave been found at spinal segments adjacent to a spinal fusion site,including disc degeneration, disc herniation, instability, spinalstenosis, spondylosis and facet joint arthritis. Consequently, manypatients may require additional disc removal and/or fusion procedures asa result of a spinal fusion. Alternatives to fusing a spinal motionsegment therefore clearly have inherent advantages.

Several different types of intervertebral disc arthroplasty devices havebeen proposed for preventing collapse of the space between adjacentvertebrae, to reduce pain and to maintain stability and range ofrotational motion between the vertebrae. For example, U.S. Pat. No.5,755,796 discloses a prosthesis for implantation in the disc spacebetween adjacent vertebrae. The prosthesis has two elements, one beingattached to the vertebra above the disc space, and the other beingattached to the vertebra below the disc space. The lower elementincludes a hollow box frame having a spherical seat inside, and theupper element includes a spherically-shaped head that fits into thespherical seat. U.S. Pat. No. 5,556,431 discloses a three-pieceintervertebral disc endoprosthesis, in which two plates, each having ahollow in one side, are fixed to adjacent vertebrae so that the twohollows face each other across the disc space. The third element is acore having an outwardly rounded surface on each side that fits into thehollows in the vertebral plates. Similarly, U.S. Pat. No. 5,684,296discloses a prosthesis having two L-shaped members, each having curvedsections between which a resilient disc body is placed.

U.S. Pat. Nos. 5,782,832 and 5,683,465 disclose implants having twoplate members anchored to adjacent vertebrae within the disc space. InU.S. Pat. No. 5,782,832, the upper plate member has a rounded undersideand the lower plate member has a hollowed top side to engage theunderside of the upper plate member and allow rotation. In U.S. Pat. No.5,683,465, the plate members have a snap-fit ball and socket engagementallowing rotation. Other prosthetic intervertebral discs are also known.Some are composite components having metal and rubber or polymer insertswhich are designed to replicate the characteristics and performance ofthe discs in separating and enabling movement of adjacent vertebrae withrespect to each other. Other designs are more mechanical in nature,including springs or other damping mechanisms also designed toapproximate the behavior of a normal disc.

The normal movement of vertebrae with respect to one another involvesvariable rotation and translation. These components of the movement aredictated by the shape and size of the individual vertebrae including therelative positions of the unconvertebral joints (in the cervical spine),the orientation of the facet joints and ligamentous constraints. Inessence the axis of rotation for any two vertebrae is unique and duringflexion or extension will shift, or translate.

The prior art describes disc prosthesis or joints that dictate a fixedaxis of rotation that will not permit translation and will thereforeprevent normal movement and tend to jam. The latter may lead toexcessive stresses on the prosthesis leading to wear or failure or betransferred to adjoining motion segments provoking pain and/oraccelerated degeneration.

Further, many prior devices are relatively difficult to implant. Mostare designed to be attached via integral anchors to the vertebralsurface facing the intervertebral disc space. To implant such a device,the adjacent vertebrae must be spread substantially further apart thantheir normal distance from each other, so that the prosthesis can bemaneuvered between the vertebrae and the anchors can be inserted intotheir respective vertebrae. Such an operation presents additional riskof injury to the vertebrae themselves from misplacement or scratching bythe anchors, and to other tissues due to the spreading of the vertebraebeyond its normal span.

Therefore, there remains a need for an intervertebral joint prosthesisallowing translational as well as rotational movement between implantedvertebrae, and which is easy to implant in a disc space. There is also aneed for a method and instrumentation for implanting such anintervertebral joint prosthesis.

SUMMARY OF THE INVENTION

The present invention is directed to an intervertebral joint prosthesishaving a ball component for engagement with a first vertebra and atrough component for engagement with a second vertebra adjacent to thefirst vertebra. The trough component includes a generally concavesurface having a substantially flat portion. When the ball component andthe trough component are engaged to their respective vertebrae, the ballcomponent and the trough component engage each other in aball-and-socket relationship permitting rotation and translation withrespect to each other. Both the ball component and the trough componentinclude a flange at one end of the component for engaging a vertebra.

The ball component includes a substantially spherically shaped convexportion which engages a substantially spherically shaped concave portionof the trough component, which concave portion also includes a flatportion. In one embodiment, the flanges of each component include holesthrough which bone screws can be fitted to attach the components totheir respective vertebrae. The flanges may be configured to conform tothe general shape of the human vertebrae.

By permitting the ball component to slide or translate in the troughcomponent the present invention enables both the axis of rotation andthe degree of translation of the joint to be dictated by the anatomicalconstraints of the motion segment within an acceptable range.

The invention also contemplates a tool for use in implanting anintervertebral joint prosthesis, having an elongated handle portion anda prosthesis-engaging portion having elements which hold the one or moreparts of the intervertebral joint prosthesis. In one embodiment, theprosthesis-engaging portion of the tool includes a central flange and/ora surface configured so that the intervertebral prosthesis or its partsare maintained in a predetermined orientation or spatial relationship.Where the intervertebral joint prosthesis includes apertures foraccommodating bone screws, the prosthesis-engaging portion of the toolpreferably includes associated apertures for drilling holes for bonescrews and/or for holding the prosthesis to the tool.

The present invention also encompasses methodology for implanting atwo-part intervertebral joint prosthesis which includes placing theprosthesis parts in a predetermined spatial relationship, inserting theparts into a disc space between two adjacent vertebrae so that one ofthe prosthesis parts abuts one of the vertebrae and the other of theprosthesis parts abuts the other of the vertebrae and so that thepredetermined spatial relationship of the prosthesis parts ismaintained, and fastening the parts to their respective vertebrae.Particular embodiments of the methodology include connecting the partsto an insertion tool in a predetermined relationship with each other,inserting the insertion tool into the body so that a portion of bothparts of the prosthesis are in a disc space between adjacent vertebrae,and fastening each part of the prosthesis to a respective vertebra. Apreferred embodiment of the fastening step includes drilling holes inthe vertebrae through apertures in the prosthesis parts and a connectedinsertion tool and threading screws through the apertures and into thebone.

The present invention provides an intervertebral joint prosthesis, andtools and methods for implantation, which allows a normal range oftranslation and rotation between the adjacent vertebrae to which theprosthesis has been fastened. The prosthesis is easy to implant via itsflanges, obviating the need for distention of the adjacent vertebrae towiden the disc space. The intervertebral joint prosthesis is alsoimplanted with a predetermined orientation of the prosthesis or spatialrelationship between its components, which reduces or eliminates theneed for in vivo adjustment. The prosthesis of the present inventionalso has a low profile and a minimal number of parts. These and otheradvantages will be clear to one of ordinary skill in the art byreference to the drawings and to the detailed description herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view, showing a side view of oneembodiment of the prosthesis of the present invention implanted betweenadjacent vertebrae shown in cross-section.

FIG. 1 a is a sectional view of the embodiment of the prosthesisillustrated in FIG. 1.

FIG. 2 is a front elevational view of an embodiment of the ballcomponent of the prosthesis illustrated in FIG. 1.

FIG. 3 is a sectional view of the ball component illustrated in FIG. 2,taken along the line 3-3 and viewed in the direction of the arrows.

FIG. 4 is a sectional view of the ball component illustrated in FIG. 2,taken along the line 4-4 and viewed in the direction of the arrows.

FIG. 5 is a perspective view of an embodiment of the trough component ofthe prosthesis illustrated in FIG. 1.

FIG. 6 is a front elevational view of an embodiment of the troughcomponent of the prosthesis illustrated in FIG. 1.

FIG. 7 is a sectional view of the trough component illustrated in FIG.5, taken along the line 7-7 in FIG. 6 and viewed in the direction of thearrows.

FIG. 8 is a sectional view of the trough component illustrated in FIG.5, taken along the line 8-8 in FIG. 6 and viewed in the direction of thearrows.

FIG. 9 is a side elevational view of an embodiment of the ball componentillustrated in FIG. 2.

FIG. 10 is a side elevational view of an embodiment of the troughcomponent illustrated in FIG. 5.

FIG. 11 is a sectional view of the ball component illustrated in FIG. 9,taken along the line 11-11 and viewed in the direction of the arrows.

FIG. 12 is a sectional view of the trough component illustrated in FIG.10, taken along the line 12-12 and viewed in the direction of thearrows.

FIG. 13 is a perspective view of one embodiment of the insertion tool ofthe present invention.

FIG. 14 a is a side view of the embodiment of the insertion toolillustrated in FIG. 13.

FIG. 14 b is a top view of the embodiment of the insertion toolillustrated in FIG. 13, rotated 90 degrees around the longitudinal axisillustrated in FIG. 14 a.

FIG. 15 a is a side view of an alternate embodiment of the insertiontool of the present invention.

FIG. 15 b is a perspective view of one embodiment of the prosthesis ofthe present invention engaged to the prosthesis engaging portion of theembodiment of the insertion tool illustrated in FIG. 15 a.

FIG. 16 is a perspective view of an embodiment of the prosthesis of thepresent invention engaged with the insertion tool illustrated in FIG.13.

FIG. 17 is a side elevational view of an embodiment of the prosthesis ofthe present invention engaged with an embodiment of the prosthesisengaging surface of the insertion tool illustrated in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein, beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring generally to FIGS. 1-12, there is shown one embodiment of theintervertebral joint prosthesis 20 of the present invention. Prosthesis20 includes a ball component 22 and a trough component 24 that areinterengagable to form prosthesis 20. In an intervertebral disc space 28between two adjacent vertebrae 26, 27, ball component 22 is fixed to oneof the adjacent vertebrae (e.g. vertebra 26 in FIG. 1), and troughcomponent 24 is fixed to the other adjacent vertebra (e.g. vertebra 27in FIG. 1) so that the components are interengaged within at least aportion of intervertebral space 28.

Ball component 22 includes a generally convex surface 30 and in oneembodiment an opposite substantially flat vertebra engaging surface 32.In a particular embodiment, generally convex surface 30 is substantiallyspherical in shape. In a specific embodiment, a wedge surface 33 isprovided at one end of vertebra engaging surface 32, which allows easierinsertion of ball component 22 into the disc space and impedes migrationof ball component 22. A flange 34 is provided at one end of ballcomponent 22 for attaching ball component 22 to a vertebra, and ispreferably formed to have a low profile and bulk. In the embodiment inwhich ball component 22 includes wedge surface 33, flange 34 is at theopposite end of ball component 22 from wedge surface 33. Flange 34includes a vertebra engaging surface 35.

In a particular embodiment of ball component 22, flange 34 includes oneor more bone screw apertures 36, and in a specific embodiment, two bonescrew apertures 36 are provided in a symmetric relationship throughflange 34. In that specific embodiment, one or more bone screws 37 (FIG.4) are threaded into the vertebra through one or more apertures 36 tofix ball component 22 to the vertebra. In the illustrated embodiment, anaperture 38 (FIGS. 2-3) is also provided through flange 34 for a lockingscrew 39 (FIG. 1). After ball component 22 is attached to the vertebraeusing bone screw(s) 37, locking screw 39 is threaded into locking screwaperture 38 in flange 34, covering the heads of bone screw(s) 37 andpreventing loosening of bone screw(s) 37 with respect to ball component22. Additionally, the illustrated embodiment of ball component 22includes indentations 40 for gripping ball component 22 by an insertiontool, as will be described further hereinafter. Preferably, indentations40 are located at the base of flange 34, where flange 34 meetssubstantially flat vertebra engaging surface 32.

Flange 34 may be angled with respect to vertebra engaging surface 32 ofball component 22. In a particularly preferred embodiment, asillustrated in FIG. 3, the internal angle A between vertebra engagingsurface 35 and vertebra engaging surface 32 is approximately 80 degrees.This angle has been found to provide a good fit with the anteriorportion of the upper vertebra in a middle or lower cervical spinalmotion segment, such as C4-C5. Ball component 22 can be constructed witha different angle between vertebra engaging surfaces 35 and 32 accordingto the vertebrae to be implanted and the needs of patients. For example,for upper cervical spinal motion segments such as C2-C3, the internalangle between vertebra engaging surface 35 and vertebra engaging surface32 may be somewhat more acute, in the range of 70-80 degrees. Flange 34may also be slightly curved from side to side, as illustrated in FIG. 4.Such curvature is particularly useful for anterior placement ofprosthesis 20, as it approximates the lateral curvature of the anteriorsurface of the human vertebra.

Trough component 24, in the embodiment illustrated, is similar in manyrespects to ball component 22. Trough component 24 includes a generallyconcave surface 50, which generally concave surface 50 includes asubstantially flat portion 52 (FIGS. 5-7). Opposite generally concavesurface 50 is a vertebra engaging surface 54, which, in the illustratedembodiment, includes a wedge surface 55 similar to wedge surface 33 ofball component 22. Trough component 24 also includes a flange 56 and aflange vertebrae engaging surface 57 which are similar to flange 34 andflange vertebra engaging surface 35 of ball component 22.

As with a particular embodiment of ball component 22, the illustratedembodiment of flange 56 of trough component 24 includes at least oneaperture 58 and preferably two symmetric apertures 58, each of which canaccommodate a bone screw 59 (FIG. 8). In that embodiment, flange 56 mayalso include a lock screw aperture 60 and lock screw 61, as describedwith respect to ball component 22. Additionally, trough component 24 inone embodiment includes indentations 62, which are similar in locationand structure to indentations 40 of ball component 22. Flange 56 oftrough component 24, in a preferred embodiment, is also angled withrespect to vertebra engaging surface 54. In the illustrated embodiment,the internal angle B between flange vertebra engaging surface 57 andvertebra engaging-surface 54 is approximately 95 degrees, which providesa good fit with the anterior portion of a lower vertebra of a middle orlower cervical spinal motion segment. As noted with respect to ballcomponent 22, trough component 24 may be manufactured with a differentangle between surfaces 57 and 54 according to the needs of the patientor other factors. For example, for upper cervical spinal motionsegments, the angle between surfaces 57 and 54 may be between 90 and 100degrees.

Referring now to FIGS. 5, 7 and 10, the generally concave surface 50 oftrough component 24 is illustrated according to one embodiment of thepresent invention. Generally concave surface 50, in this embodiment,includes a substantially flat (in that it is cylindrical rather thanspherical) surface 52 that is approximately centrally located ongenerally concave surface 50. In a specific embodiment, generallyconcave surface 50 includes substantially spherical surfaces 64 on bothsides of substantially flat surface 52. Substantially flat surface 52may be of any desired geometrical configuration, though in a currentlypreferred embodiment, substantially flat surface 52 is in the shape of arectangle, analogous to a slot in generally concave surface 50, and isapproximately parallel to flange 56. In a particular preferredembodiment of ball component 22 and trough component 24, the radius ofgenerally convex surface 30 and of the spherical portion of generallyconcave surface 50 is approximately the same.

In use, ball component 22 and trough component 24 are attached toadjacent vertebrae so that a portion of components 22, 24 are within thedisc space and engage each other to provide a ball-and-socketarrangement which permits rotation and translation of the components,and thereby the vertebrae to which they are fixed with respect to eachother. To accomplish that, when prosthesis 20 is implanted generallyconvex surface 30 of ball component 22 engages generally concave surface50 of trough component 24. When engaged with generally concave surface50, generally convex surface 30 can rotate in any direction. Whengenerally convex surface 30 is in contact with substantially flatportion 52 of generally concave surface 50, generally convex surface 30can move along substantially flat portion 52 in translation, as well asrotate with respect to generally concave surface 50. In a specificembodiment of prosthesis 20, ball component 22 is an “upper” componentand is fixed to the vertebra immediately above or superior to the discspace (i.e. the vertebra closer to the head). In that embodiment, troughcomponent 24 is attached to the lower or inferior vertebra (i.e. thevertebra closer to the coccyx). Thus, with ball component 22 attached toone vertebra and trough component 24 attached to an adjacent vertebra sothat generally convex surface 30 and generally concave surface 50 areengaged, prosthesis 20 permits the adjacent vertebrae to rotate andtranslate with respect to each other, providing a normal range ofintervertebral joint motion.

The present invention also comprehends an insertion tool 70 for use inimplanting joint prosthesis 20. As illustrated in FIGS. 13-17, insertiontool 70 in one embodiment includes an elongated handle portion 72integral with or attached to an extension portion 74. Aprosthesis-engaging portion 76 is attached at the end of extensionportion 74. Prosthesis-engaging portion 76 includes prosthesis-engagingsurface 78. Prosthesis-engaging surface 78, in the illustratedembodiment, includes a central separator flange 79. The illustratedembodiment of prosthesis-engaging portion 76 also includes a set ofapertures 80. This embodiment of insertion tool 70 is intended for usewith the embodiment of ball component 22 and trough component 24 havingbone screw aperture(s) 36 and 58, respectively, and apertures 80 ofprosthesis-engaging portion 76 are configured so as to communicate withaperture(s) 36 of ball component 22 and aperture(s) 58 of troughcomponent 24. In that embodiment, apertures 80 are sized slightly largerthan the head(s) of bone screw(s) 37, so that screw(s) 37 may beinserted through apertures 80 to fix components 22 and 24 of prosthesis20 to their respective vertebrae without also fixing tool 70 thereto.

Prosthesis-engaging portion 76 of insertion tool 70 is also capable ofretaining prosthesis 20 in engagement with prosthesis-engaging portion76. The illustrated embodiment of prosthesis-engaging portion 76 alsoincludes a pair of clips 82 on both sides of prosthesis-engaging portion76. Clips 82 are designed to hold the embodiments of ball component 22and trough component 24 that include indentations 40 and 62,respectively. Each clip 82 is attached to prosthesis engaging portion76, and includes two clip fingers 84 each having a thickened portion 86for insertion into indentations 40 of ball component 22 and indentations62 of trough component 24. In an alternative embodiment of insertiontool 70 (FIGS. 15 a-15 b), prosthesis-engaging portion 76 is providedwith apertures 80, and a pair of cam screws 90 which extend through oneaperture 80 on each side of separator flange 79. Ball component 22 andtrough component 24, in the embodiment in which they include bone screwapertures 36 and 58, respectively, are engaged to prosthesis engagingsurface 78 so that apertures 36 and 58 communicate with apertures 80 ofprosthesis engaging portion 76. Cam screws 90 are then inserted into oneof apertures 36 and one of apertures 58 to lock ball component 22 andtrough component 24 to prosthesis engagement surface 76.

As illustrated in FIGS. 14 a-17, a particular embodiment ofprosthesis-engaging portion 76 is configured to maintain ball component22 and trough component 24 in a predetermined spatial relationship orneutral position so as to insure correct alignment and positioning ofthe components with respect to each other and with respect to disc spaceand vertebrae into which they are to be implanted. Separator flange 79of prosthesis engaging portion 76 is configured to fit between and toinsure the proper spacing between ball component 22 and trough component24. Prosthesis-engaging surface 78 is angled so that, in cooperationwith separator flange 79, prosthesis-engaging portion 76 holds ballcomponent 22 and trough component 24 in a precise predetermined spatialrelationship with each other. For example, in the embodiments describedabove in which vertebra engaging surfaces 32 and 35 of ball component 22have an internal angle of 80 degrees, prosthesis engaging surface 78will include a portion forming an internal angle of approximately 80degrees with separator flange 79. Similarly, in the embodiment of troughcomponent 24 in which vertebra engaging surfaces 54 and 57 have aninternal angle of approximately 95 degrees, prosthesis engaging surface78 will include a portion which forms an internal angle of approximately95 degrees with separator flange 79. Ball component 22 and troughcomponent 24 are thereby held for implantation together such thatvertebra engaging surface 32 of ball component 22 and vertebra engagingsurface 54 of trough component 24 are approximately parallel, and suchthat convex surface 30 is engaged with concave surface 50.

Insertion tool 70 has been described above primarily with respect to theembodiments of prosthesis 20 described herein. Nonetheless, one ofordinary skill in the art will appreciate that insertion tool 70 may beuseful with other prostheses that must be held in a particularpredetermined orientation, or that have parts that must be retained in aparticular spatial relationship.

After an intervertebral disc is resected and/or the disc space isprepared, the intervertebral joint prosthesis 20 of the presentinvention may be implanted. Ball component 22 and trough component 24 ofjoint prosthesis 20 are placed in a predetermined relationship with eachother, preferably by engagement to insertion tool 70 of the presentinvention or an equivalent tool. Components 22 and 24, held in apredetermined spatial relationship, are then inserted into the body sothat vertebra engaging surfaces 32 and 54 are within the disc space. Inthe embodiments of components 22 and 24 that include a wedge surface 33and 55, respectively, wedge surfaces 33 and 55 enable easierimplantation of prosthesis 20 by forcing the adjacent vertebrae apartslightly, if necessary, as components 22 and 24 are advanced into thedisc space. Once components 22 and 24 are inserted into the disc space,wedge surfaces 33 and 55 grip their respective vertebrae to impede orprevent migration of prosthesis 20.

When prosthesis 20 is in place between the vertebrae, components 22 and24 are attached to the vertebrae, in one embodiment via flanges 34 and56. In the embodiment of the present invention in which flanges 34 and56 include bone screw apertures 36 and 58, respectively, attachment ofthe components 22 and 24 to the vertebrae may be accomplished bydrilling through apertures 36 and 58 into the vertebrae. The drill isthen removed and bone screws are threaded into the vertebrae throughapertures 36 and 58, thereby fixing components 22 and 24 to theirrespective vertebrae. When all holes have been drilled and all screws 37have been threaded into the vertebrae, insertion tool 70 is removed (ifone has been used), locking screws may be threaded into apertures 38 and60 (if present in components 22 and 24), and the operation is concluded.

A specific embodiment of the method of implanting the joint prosthesis20 includes use of an embodiment of insertion tool 70. In the methodusing the embodiment of insertion tool 70 having four apertures 80 and aclip 82 on both sides of prosthesis engaging portion 76, components 22and 24 of joint prosthesis 20 are engaged to insertion tool 70 in apredetermined spatial relationship as described above. Insertion tool 70is inserted into the body so that joint prosthesis 20 is in the discspace between adjacent vertebrae. A drill (and a drill sleeve, ifnecessary) is inserted through an aperture 80 in prosthesis engagingportion 76 and through an aperture 36 or 58 of component 22 or component24 communicating with the aperture 80, and a hole is drilled in theunderlying vertebra. The drilling procedure is repeated for each of theapertures 80 in prosthesis engaging portion 76 which communicate with anaperture 36 or 58 in ball component 22 or trough component 24,respectively. Screws 37 are threaded into the vertebrae throughapertures 80 and apertures 36 and 58, fixing components 22 and 24 totheir respective vertebrae. Apertures 80 of prosthesis engaging portion76 are sized slightly larger than the heads of the bone screws 37 usedto attach components 22 and 24 to their respective vertebrae. When allof the holes have been drilled and all of the screws have been threadedinto the bone, clips 82 are disengaged from components 22 and 24 andinsertion tool 70 is removed. Similarly, in the embodiment of insertiontool 70 illustrated in FIGS. 15 a-15 b having cam screws 90, components22 and 24 are attached to prosthesis-engaging portion 76 by locking camscrews 90 into one each of apertures 36 and 58. Holes are drilledthrough apertures 80 and apertures 36 and 58 not occupied by cam screws90. After such holes are drilled, screws are threaded into such vertebraholes. The cam screws are then unlocked, the insertion tool 70 isremoved and the remaining holes are drilled through apertures 36 and 58in components 22 and 24. Bone screws 37 are threaded-into the vertebraethrough components 22 and 24 to complete the fixation of components 22and 24 to their respective vertebrae.

The devices and methods of the present invention are currently believedto be most useful in repairing vertebral joints in the cervical region.Nevertheless, it is believed that the devices and methods of the presentinvention could also be useful in repairing other spinal motion segmentsas well.

In the embodiments of ball component 22 and trough component 24 whichinclude a locking screw aperture 38 and 60, respectively, fixation ofjoint prosthesis 20 is completed by threading a locking screw (notshown) into apertures 38 and 60. When components 22 and 24 of jointprosthesis 20 are satisfactorily fixed, the operation may be concluded.

The attachment of components 22 and 24 to vertebrae has been primarilydescribed through use of bone screws fixing the components to thevertebrae. It is understood that alternative attachment structures ormethods may be used, such as by stapling or by applying adhesive tovertebra engaging surfaces 32, 35, 54 and/or 57, so long as components22 and 24 are firmly fixed to their respective vertebrae so as towithstand the stresses inherent in continual rotational andtranslational movements. Further, joint prosthesis 20, as well as thebone screws or other structures used to implant them within the body,are preferably made of biocompatible materials such as stainless steel,titanium, or other known biocompatible materials or their equivalents.Insertion tool 70 can be made of any appropriate material, althoughstainless steel is preferred.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

1. A combination of a tool and an intervertebral joint prosthesis, thecombination comprising: an intervertebral joint prosthesis including afirst member and a second member distinct from the first member, thefirst member including a first aperture extending therethrough, thesecond member including a second aperture extending therethrough; anelongated handle portion; a prosthesis engaging portion connected tosaid handle portion for holding the prosthesis, said prosthesis engagingportion having a first side facing the elongated handle portion and asecond side effective to engage the prosthesis, the prosthesis engagingportion further includes a plurality of apertures which communicate withthe apertures of the prosthesis, said apertures extending from the firstside to the second side: and a plurality of clips connected to saidprosthesis engaging portion for retaining the prosthesis in engagementwith said prosthesis engaging portion.
 2. The combination of claim 1,wherein said prosthesis engaging portion includes a prosthesis engagingsurface for maintaining the prosthesis in a predetermined orientation.3. The combination of claim 2, wherein said prosthesis engaging surfaceincludes at least one portion configured at an oblique angle to saidhandle portion.
 4. The combination of claim 2, wherein said prosthesisengaging surface includes a flange.
 5. The combination of claim 4,wherein said prosthesis engaging surface includes at least one surfaceportion abutting said flange configured at an oblique angle to saidhandle portion.
 6. The combination of claim 4, wherein said flange isapproximately centrally located on said prosthesis engaging surface. 7.The combination of claim 4, wherein said handle has a longitudinal axis,and said flange intersects said longitudinal axis.
 8. The combination ofclaim 4 wherein the flange is at least partially between said first andsecond members.
 9. The combination of claim 4, wherein said handleportion is a single piece.
 10. The combination tool of claim 1, whereineach of said clips include two distally-extending fingers, each having athickened portion for insertion into respective indentations of thefirst and second members.
 11. A combination of a tool and anintervertebral joint prosthesis having a first member part to beattached to an upper vertebra and a second member part to be fixed to alower vertebra, said combination comprising said parts each including atleast one aperture, said combination further comprising: anintervertebral joint prosthesis including a first member and a secondmember distinct from the first member, the first member including afirst aperture extending therethrough, the second member including asecond aperture extending therethrough; an elongated handle portion; aprosthesis engaging portion connected to said handle portion, saidprosthesis engaging portion having a first side facing the elongatedhandle portion and a second side effective to engage the prosthesis, theprosthesis engaging portion further having a plurality of apertureswhich communicate with said apertures of said prosthesis and extend fromthe first side to the second side; a plurality of clip members connectedto said prosthesis engaging portion for retaining the prosthesis partsin engagement with said prosthesis engaging portion; and means connectedto said prosthesis engaging portion for maintaining the prosthesis partsin a predetermined spatial relationship.
 12. The combination of claim11, wherein said clip members are adapted to simultaneously engage thefirst and second members.
 13. The combination of claim 11, wherein saidprosthesis engaging portion includes a prosthesis engaging surface formaintaining the prosthesis in a predetermined orientation.
 14. Thecombination of claim 13, wherein said prosthesis engaging surfaceincludes at least one portion configured at an oblique angle to saidhandle portion.
 15. The combination of claim 13, wherein said prosthesisengaging surface includes a flange.
 16. The combination of claim 15,wherein said prosthesis engaging surface includes at least one surfaceportion abutting said flange configured at an oblique angle to saidhandle portion.
 17. The combination of claim 15, wherein said flange isapproximately centrally located on said prosthesis engaging surface. 18.The combination of claim 15, wherein said handle has a longitudinalaxis, and said flange intersects said longitudinal axis.
 19. Thecombination of claim 11, wherein said handle portion is a single piece.20. The combination of claim 11, wherein the flange is at leastpartially between said first and second members.
 21. A tool for use inimplanting an intervertebral joint prosthesis, the tool comprising: anelongated handle portion; a prosthesis engaging portion connected tosaid handle portion for holding the intervertebral joint prosthesis, theprosthesis engaging portion having a first side facing the elongatedhandle portion and a second side effective to engage the prosthesis, theprosthesis engaging portion further having a plurality of apertureseffective to communicate with apertures of said prosthesis and extendfrom the first side to the second side; and at least one clip connectedto said prosthesis engaging portion for retaining the prosthesis inengagement with said prosthesis engaging portion, said at least one cliphaving a portion immovably fixed to said prosthesis engaging portion.22. The tool of claim 21, wherein said prosthesis engaging portionincludes a prosthesis engaging surface for maintaining the prosthesis ina predetermined orientation.
 23. The tool of claim 22, wherein saidprosthesis engaging surface includes at least one portion configured atan oblique angle to said handle portion.
 24. The tool of claim 22,wherein said prosthesis engaging surface includes a flange.
 25. The toolof claim 24, wherein said prosthesis engaging surface includes at leastone surface portion abutting said flange configured at an oblique angleto said handle portion.
 26. The tool of claim 24, wherein said handlehas a longitudinal axis, and said flange intersects said longitudinalaxis.
 27. The tool of claim 24, wherein, said flange is at leastpartially between said first and second members.
 28. The tool of claim21, wherein said handle portion is a single piece.
 29. The combinationof claim 21, wherein said prosthesis engaging portion has a proximalsurface connected to said handle portion and side surfaces opposed toeach other and substantially perpendicular to said proximal surface, andwherein said at least one clip is fixed to one of said side surfaces.30. A tool for use in implanting an intervertebral joint prosthesishaving a first member to be attached to an upper vertebra and a secondmember to be fixed to a lower vertebra, said parts each including atleast one aperture, said tool comprising: an elongated handle portion; aprosthesis engaging portion connected to said handle portion, saidprosthesis engaging portion having a first side facing the elongatedhandle portion and a second side effective to engage the prosthesis, theprosthesis engaging portion further having a plurality of apertureseffective to communicate with apertures of said prosthesis and extendfrom the first side to the second side, the prosthesis engaging portionhaving a flange with a long dimension, said apertures of said prosthesisengaging portion being offset from said flange; and at least one clipconnected to said prosthesis engaging portion for retaining theprosthesis parts in engagement with said prosthesis engaging portion.31. The tool of claim 30, wherein said prosthesis engaging surfaceincludes at least one portion configured at an oblique angle to saidhandle portion.
 32. The tool of claim 30, wherein said prosthesisengaging surface includes a flange.
 33. The tool of claim 32, whereinsaid flange is approximately centrally located on said prosthesisengaging surface.
 34. The tool of claim 32, wherein said prosthesisengaging surface includes at least one surface portion abutting saidflange configured at an oblique angle to said handle portion.
 35. Thecombination of claim 30, wherein said at least one clip member isadapted to simultaneously engage the first and second members.